1. Field of Invention
The present invention relates to a semiconductor process. More particularly, the present invention relates to an improved method of filling gap with dielectrics.
2. Description of Related Art
With the increasing integration in integrated circuits (IC), a conventional wafer can no longer provide sufficient area for interconnects. In order to satisfy performance requirements, design rules of forming more than two metal layers for interconnects are gradually applied in integrated circuits. An inter-metal dielectric (IMD) layer is formed between two metal layers for isolation. Since a metal layer and a dielectric layer are alternately laminated to form metal interconnects, planarization and quality of the dielectric layer play an important role in semiconductor fabrication. If the result of the planarization is not ideal, the uneven surface of the dielectric layer causes misalignment when a subsequent photolithography process is performed so that the pattern cannot accurately transfer onto the metal line and the process becomes more difficult.
As device integration is increased, density of conductive lines is also increased. A gap is formed between every two neighboring conductive lines. While depositing a dielectric film of silicon oxide in a region with a high patterned density of the conductive lines, depositing rates on top of the conductive line, on sidewalls of the gap, and on the bottom of the gap are all different. Thus voids are easily generated in the silicon oxide layer. Voids in the silicon oxide layer seriously affect the device quality. While subsequently performing a chemical-mechanical polishing (CMP) step to planarize the silicon oxide layer, the voids are exposed so that slurry easily flows into these voids. Consequently, it is difficult to clean the slurry in the voids, which leads to contamination of the dielectrics. Device yield is thus decreased.
In order to solve aforementioned problems, a conventional method provides a nitrogen plasma treatment. However, the nitrogen plasma treatment needs one additional photomask and photoresist step so as to increase capital expenditure.